Your mother seems to be suffering from peripheral neuropathy and the causes could be long standing diabetes
or even a deficiency of VIT B12.
VIT B12 deficiency is very common in people taking METFORMIN
and in vegetarians,specially vegans.
I advise you to get her injectable VIT B 12 for two weeks and see the response.
Failure to respond to injectable VIT B12 would indirectly confirm that symptoms are most likely due to diabetic peripheral neuropathy
Although there has been considerable advances in the understanding behind the development of neuropathy but their treatment has been limited.
Along with a meticulous and tight control of blood sugar levels,treatment is aimed at reducing pain and other associated symptoms.
This is achieved by use of antidepressants like DULOXETIN ,use of anticonvulsant like PREGABALIN
and a long acting opioid like TAPENTADOL
You must discuss with your doctor to use these drugs singly or in different combinations.
I hope it helps.